The present disclosure is related to lithography, and more particularly to the design and manufacture of a surface which may be a reticle, a wafer, or any other surface, using charged particle beam lithography.
In the production or manufacturing of semiconductor devices, such as integrated circuits, optical lithography may be used to fabricate the semiconductor devices. Optical lithography is a printing process in which a lithographic mask or photomask manufactured from a reticle is used to transfer patterns to a substrate such as a semiconductor or silicon wafer to create the integrated circuit. Other substrates could include flat panel displays or even other reticles. Also, extreme ultraviolet (EUV) or X-ray lithography are considered types of optical lithography. The reticle or multiple reticles may contain a circuit pattern corresponding to an individual layer of the integrated circuit and this pattern can be imaged onto a certain area on the substrate that has been coated with a layer of radiation-sensitive material known as photoresist or resist. Once the patterned layer is transferred the layer may undergo various other processes such as etching, ion-implantation (doping), metallization, oxidation, and polishing. These processes are employed to finish an individual layer in the substrate. If several layers are required, then the whole process or variations thereof will be repeated for each new layer. Eventually, a combination of multiples of devices or integrated circuits will be present on the substrate. These integrated circuits may then be separated from one another by dicing or sawing and then may be mounted into individual packages. In the more general case, the patterns on the substrate may be used to define artifacts such as display pixels or magnetic recording heads.
In the production or manufacturing of semiconductor devices, such as integrated circuits, maskless direct write may also be used to fabricate the semiconductor devices. Maskless direct write is a printing process in which charged particle beam lithography is used to transfer patterns to a substrate such as a semiconductor or silicon wafer to create the integrated circuit. Other substrates could include flat panel displays, imprint masks for nano-imprinting, or even reticles. Desired patterns of a layer are written directly on the surface, which in this case is also the substrate. Once the patterned layer is transferred the layer may undergo various other processes such as etching, ion-implantation (doping), metallization, oxidation, and polishing. These processes are employed to finish an individual layer in the substrate. If several layers are required, then the whole process or variations thereof will be repeated for each new layer. Some of the layers may be written using optical lithography while others may be written using maskless direct write to fabricate the same substrate. Eventually, a combination of multiples of devices or integrated circuits will be present on the substrate. These integrated circuits are then separated from one another by dicing or sawing and then mounted into individual packages. In the more general case, the patterns on the surface may be used to define artifacts such as display pixels or magnetic recording heads.
In semiconductor manufacturing, reliably manufacturing contacts and vias is difficult and important, especially when optical lithography is used to manufacture patterns smaller than 80 nm half pitch, where half pitch is one-half of the minimum contact or via size plus one-half of the minimum required space between contacts or vias. Contacts and vias connect a conductive material on one layer to another conductive material on another layer. In older technology nodes which were relatively larger than currently-popular technology nodes, attempts were made to manufacture square vias and contacts on the wafer. Square contacts and vias are desirable so as to maximize the amount of area that connects between the conductive material in the below layer and the conductive material in the above layer. But with decreasing feature sizes, it has become prohibitively expensive or impractical to create large numbers of square patterns on the semiconductor wafer. Especially at 80 nm half pitch and below, semiconductor manufacturers target forming near-circles on the wafer, when viewed from above, which create nearly cylindrical contacts or vias. The design data that specifies the desired wafer shape still specifies the desired shape as a square. However, the manufacturers and designers alike work with the assumption that limitations of the optical lithographic process will cause the actual resulting shape to be a near-circle on the wafer. The generalized case of this effect for all shapes is sometimes referred to as corner rounding.
A significant advantage to the conventional practice of specifying contacts and vias as squares in the design data is that square patterns can be formed relatively quickly on a reticle. The use of square patterns for contacts and vias on the reticle and photomask, however, make the manufacturing of vias and contacts on the semiconductor device more difficult. It would be advantageous to eliminate the manufacturing difficulties associated with using square patterns on a photomask for contacts and vias, particularly for half-pitches less than 80 nm.